The disorder known as keratoconjunctivitis sicca (hereinafter KCS) was previously believed to generate its symptoms due to the formation of dry spots or incomplete wetting of the ocular surface. More recent work has shown that this theory is probably incorrect. The concept of the symptoms of the disease being due to an increased concentration of sodium chloride in the tear film was first postulated by Balik (Am. J. Ophthalmol 35, 773 (1952). Although Balik automatically rejected this postulate since he was unable to demonstrate the increase, support for this postulate was ultimately provided by Mishima et al (Ophthalmology, Proceedings of the XXI International Congress, Mexico, DF 8-14 March, 1970; Amsterdam, Excerpta Medica, 1971, pt 2, pp 1801 through 1805).
In the results obtained by Applicant and co-workers (Gilbard et al), Arch Ophthalmol 96 677, 1978, it was shown that in the 38 samples taken from 33 normal eyes a tear osmolarity of 304.+-.10.4 mOsm/l. was obtained while in the 38 samples from 30 KCS eyes osmolarity of 343.+-.32.3 mOsm/l. was obtained. By comparison it is noted that 8 eyes showing conjunctivitis (but not KCS) had a tear osmolarity of 298.+-.6.l mOsm/l.
It has been postulated that the actual value of tear film osmolarity is a function of tear secretion and evaporation. Thus, if there is a decrease in the rate of tear secretion, tear film osmolarity will rise as the volume of freshly secreted isotonic tear fluid becomes inadequate to overcome the tendency of evaporation to increase tear film osmolarity.
In order to quantify the change in tear film osmolarity, Applicant developed a new appratus and method of using same for measuring tear film osmolarity which is reported in the foregoing reference (Arch Ophthalmol 96 677, 1978).